Pressure fluid operated pumping mechanism



July 4, 1961 R. P. VINCENT 2,990,816

PRESSURE FLUID OPERATED PUMPING MECHANISM Filed March 5, 1959 2 Sheets-Sheet 1 N IO RENIC P. VINCENT INVENTOR.

ATTORNEY July 4, 1961 R: P. VINCENT PRESSURE FLUID OPERATED PUMPING MECHANISM Filed March 5, 1959 2 Sheets-Sheet 2 RENIC P. VINCENT INVENTOR.

A r TOR/VEY United States Patent 2,990,816 PRESSURE FLUID OPERATED PUMPING MECHANISM Renic Price Vincent, 3368 S. Erie, Tulsa, Okla. Filed Mar. 5, 1959, Ser. No. 797,376 23 Claims. (Cl. 121-164) This invention relates to pumping apparatus and more particularly to pumping mechanism of the reciprocating type which is adapted to be operated by fluid under pressure.

In the operation of wells, pumps of the reciprocating piston type are frequently employed which are locatedv in the well and operated from the surface by means of a polish rod connected to a string of sucker rods extending to the pump. Various types of apparatus are employed for the operation of such pumps and include mechanical beam-type and hydraulic means for lifting the rod string to accomplish the upstroke of the pump, while the downstroke of the pump takes place under the influence of the weight of the rod string. Undersome conditions, as in the pumping of deep wells where the weight of the rod 2,990,816 Patented July 4, 1961 sure fluid operated pumping mechanism where by the downward movement of the piston and rod string may be slow relative to the upstroke movement for the efiicient pumping of wells.

An important object is the provision of a hydraulic engine having a cylinder in which a piston is reciprocable string is relatively great, counterbalancing is provided for apparatus of this kind possesses the advantage of obtaining a long stroke, but also possesses the disadvantage that the system cannot be easily counterbalanced.

The present invention has for an important object the provision of a pressure fluid operated pumping mechanism of the reciprocating type wherein the advantage of a relatively long pump stroke is obtained with a counterbalancing means provided to substantially reduce the power requirements found in pumps of this type as heretofore constructed.

Another object of this invention is to provide a pressure fluid operated pumping mechanism having a counterbalance means equal to the weight of the rod string used to reciprocate the pump. 7

Another object of the invention is to provide a pressure fluid operated pumping mechanism of the reciprocating type embodying means for storing energy resulting from the downstroke of the pump, utilizing such stored energy to lift the fluid load imposed on the rod string by the sub surface pump during the upstroke of the pump, and in addition, automatic means for maintaining the stored energy between predetermined and/ or present energy levels.

A further object of the invention is to provide pressure fluid operated pumping mechanism of the reciprocating type having a pressure cylinder and a piston movably positioned in the cylinder and connected to the polish rod of the pump and including means for introducing fluid under pressure into the cylinder beneath the piston to move the piston, polish rod, and fluid load upwardly and means for storing up the energy of the fluid in the cylinder beneath the piston upon downward movement of the 7 having a pressure cylinder and a piston movably posi tioned in the cylinder and connected to the polish rod of the pump and including means for introducing fluid under relative to a head having valved passages through which pressure fluid, for actuating the piston, is introduced into and exhausted from the cylinder. 7

A still further object of this invention is to provide a hydraulic engine having means for dampening movement of a reciprocating piston within a cylinder at each end of the stroke. v

An even further object is to provide a hydraulic engine wherein a valve for interrupting flow of pressure fluid to reciprocate a piston within a cylinder is operable by mechanical and hydraulic means. v

The above and other important objects and advantages of the invention will become apparent from the following detailed description, when considered in conjunction with the annexed drawings in which:

FIGURE 1 is a diagrammatic view, illustrating the surface equipment used to carry out the preferred embodiment of the invention;

FIGURE 2 is a cross-sectional view of the power cylinder of the invention during upstroke of the pump;

FIGURE 3 is a view similar to that of FIGURE 2, showing the arrangement of parts in the power cylinder when the pump is near the bottom of the downstroke;

FIGURE 4 is a cross-sectional view taken along the line 4--4 of FIGURE 2;

FIGURE 5 is a cross-sectional view taken along the line 5-5 of FIGURE 2; and

FIGURE 6 is a cross-sectional view taken along the line 66 of FIGURE 2.

FIGURE 7 is a cross-sectional view of the mechanical-1y tripped, snap acting and hydraulically held valve used in this invention.

Description Referring now to FIGURE 1, the invention is illustrated herein in connection with its application to pumping equipment, such as a reciprocating pump of the kind commonly employed in oil Wells. Typically, the pump is operated by a polish rod, such as the rod 10, whose upper end extends above the surface and whose lower end is connected by the usual sucker rod string to the pump located in a well, not shown. The pressure fluid operated pumping mechanism of this invention includes a power cylinder 12 adapted to be supported in a vertical position as, for example, to tubular support 14, above the upper end of the well and into whose lower end the polish rod 10 is movably extended.

Near the upper end of the power cylinder 12 is an annular manifold 16 connected to a source of pressure fluid such as from discharge line 18 of pump 20. The upper end of the cylinder is closed by tubular head 22 and cap 24. Exhaust or outlet conduit 26 returns pressure fluid 27 to accumulator or surge tank 28, which is connected to the inlet of pump 20 through conduit 30. Conduit 32 interconnects the power cylinder through support 14 and another source of pressure fluid in tank 34 through control valve 36. The valve opening is adjustable automatically or manually, as shown, using valve rod handle 38 on stem 37. Spring 40, actingbetween valve 36 and end shoulder 41 maintains a fixed opening during flow of pressure fluid from tank 34 to power cylinder 12 while reversed flow will tend to slide the valve 36 on stem 37 against the spring allowing increased flow volume into tank 34. Within tank 34 is a non-compressible liquid 42 such as hydraulic oil and a compressible fluid 44, such as air, or preferably an inert gas, such as nitrogen. The non-compressible liquid 42, being more viscous than gas 44, forms a liquid seal and, in addition, provides lubrication to the moving parts within cylinder12.

In order to maintain a constant predetermined pressure of compressible gas within the system 44, an auxiliary supply tank 46 is used. The supply tank is connected to pressure tank 34 by conduits 48 and 50. Interconnecting these two lines is a first by-pass 52, having a pressure regulator 54 therein. A second by-pass line 56 interconnects line 48 to line 50 through check valve 58, chamber 62 of compressor 64, and check valve 60*. Relatively small diameter chamber 62 interconnects with large diameter chamber 66. Piston 68 is reciprocable in each chamber and comprises corresponding small and large surface area pistons. The larger chamber 66 is connected with the discharge conduit 18 of pump 20 through conduit 70 to one side of the piston. An alternate additional conduit, not shown, connects exhaust line 26 with the portion of chamber 66 on the opposite side of piston 68.

A detailed description of the power cylinder used according to this invention is shown in the remaining figures. At its lower end, the power cylinder is closed and supported by tubular member 14, through which polish rod is slidably extended through packing material 80 to form a seal between the rod and support. The power cylinder 12 is aflixed to support 14 using an internal flange 82 held in place by snap-ring 84. An O-ring seal is provided at 86. Threadably attached to polish rod 10 'is piston 88 separating the power cylinder 12, using O-ring seal 90, into a lower chamber 92, and the upper chamber 94. Throttling member 96, attached to piston 88, and extending into the upper chamber 94, is used to dampen movement of the piston 88 as it approaches the top of its upward stroke. Tubular head 22 is secured to cylinder 12 using an internal flange portion 98 and held thereto with snap-ring 102. An O-ring seal is located at 100 between the flange and cylinder wall. Alternately, the tubular head may be secured in the cylinder by any removable connection such as threads.

Inlet manifold 16 is positioned near the upper end of cylinder 12 opposite chamber 94 and valve body 104 located in cylinder 12. The body is spaced from upper flange 98 by cylinder portion 106 and spacer ring 108, and sealed with O-ring packing 110. Manifold 16 forms an annular space 116 about a multiplicity of perforations 117 and is sealed outside cylinder 12 with O-ring packing 112 and 114.

Space 116 is connected to a source of pressure fluid such as pump discharge line 18. Pressure fluid enters into the upper chamber 94 about the lower portion of the body 104. The chamber connects with upper manifold 129 and one or more outlet ports 130 through one or more passageways or valve seats 131. Valve 120, shown in cross-section at FIGURE 7, moveably operates in each passageway to close a corresponding passageway 131. The valve includes upper and lower extensions 122 and 124. A small pilot opening, shown by numeral 126, extends down through the upper extensions 122 and main valve body 120, the importance of which will be hereinafter described. Inclusive within the lower portion of valve body 104 are a multiplicity of ball check valves, generallvindicated at 132, and retained within its cage by pin 134.

Threadably connected to piston 88 is upper control rod 140, which passes through valve body 104 in sliding relationship through packing 1 42 The rod extends into tubular head 22 and has slidably disposed thereon a control piston 144 and sleeve 146. Cushion spring 148 is disposed between sleeve 146 and the interior of piston 144. The piston is adapted to provide a relatively close fit with the smaller internal diameter of tapered cylinder 150 formed in the lower interior of tubular head 22. This design provides a throttling effect to dampen movement of the piston 88 at the beginning of its upward movement.

Disposed between outlet port and tubular head 22 is disk 152 slidably disposed about upper control rod 140. This disk has a multiplicity of perforations so as to permit the passage of exhaust fluids to the outlet conduit 26.

The control rod extends upwardly into tubular head 22, and is provided at its upper end with nut 154 which contacts sleeve 146 during part of the cycle.

Operation Basically, a pneumatic pressure on the bottom of the piston lifts the combined rod string and fluid load upward. The combined rod weight assisted by the hydraulic pressure on top of the piston moves the piston down. Theoretically, the hydraulic pressure is substantially equal to the fluid load absent any friction considerations. During the downstroke, the energy is transferred and stored in the pneumatic system. The cycle is repeated by the tripping of a valve at the end of each stroke, which controls the direction of flow of hydraulic pressure.

Specific operation of the apparatus just described may be had by referring first to FIGURE 1, in conjunction with FIGURE 2. The highly compressed gas 44 in pressure tank 34 forces the non-compressible liquid 42 into the lower chamber of the power cylinder, causing upward movement of piston 88 and its attached load. Coincident with this upward movement is the closing of check valve or valves 132, forcing movement of pressuring fluids both from chamber 94 and that entering from chamber 116, through open passageways or valve seats 131, thence into outlet manifold 129 and through outlet ports 130. Fluid movement continues through perforations in plate 152, cylinder 150, and exhaust conduit 26 to tank 28 for recycle.

Piston 88 continues upward until mechanical engagement is made with lower extension 124 of valve or valves 120. In order to prevent rapid deceleration of the piston and a water-hammer elfect in the fluid conduits, before and coincident with closing of passageways 131 by the valves, 21 throttling or cushioning action is provided as the piston approaches the lower extensions 124 of valves 120. This occurs when member '96 rises into the annular space formed about a downwardly tapered valve body 104. Alternately, the lower valve body portion may be cylindrical with a tapered member slidable in the annular space thereabout.

FIGURE 3 illustrates the valve in its upper, closed position with corresponding downward piston movement. Pressure fluid from discharge line 18 of pump 20 now enters chamber 116 and into upper chamber 94 above the piston, forcing check valve 132 open. Coincident with this downward movement is the reversal of fluid movement from lower chamber 92, through line 32 into pressure tank 32, recompressing the gas therein forming the pneumatic spring of this invention. As the piston 88 approaches lower dead center, control rod 140, moving with piston 88, causes adjusting nut 154 into mechanical engagement with sleeve 146. Spring-loaded piston 148 is previously at rest in tapered outlet 150, on disk 152 in engagement with upper valve extension 122.

Further downward movement partially compresses spring 144 until suflicient pressure moves valve 120 downward to open passageway 131. This completes a cycle of operation and the process is repeated. As the piston 88, starts its upward movement, further waterhammer in the system is prevented. A gradual accelera- 5 tion of piston 8 occurs by the-throttling effect of springloaded piston 148 rising in tapered outlet 150 until it reaches a full-open position similar to that illustrated in FIGURE 2.

In those instances where atmospheric conditions, leakage, etc., cause effective changes in the working pressure of the compressible gas in pressure tank 34, a re-pressuring or compressor system is provided. Pressure regulator 54, between line 50 and 48, maintains a constant pressure in tank 34. Line 50 is connected auxiliary supply tank 46 and normally maintained at a greater pressure than that in pressure tank 34.

During the downstroke of piston 88 in power cylinder 12, the liquid in line 70 from the discharge of pump 20, is at arelatively high pressure. The fluid enters chamber 66 of the compressor, forcing piston .68 upward, compressing the gas in upper chamber 62. 7 Upon compression of the gas to an amount of greater than that existing in line 50 from auxiliary tank 46, check valve 60 will open allowing the gas to pass through. During the upward stroke the pressure in line 70 is decreased and piston 68 moves downward under the action gas passing through check valve 6 8 into chamber 62. The cycle is repeated with each stroke of power piston 88. An auxiliary conduit, not shown, is provided from exhaust line 26, connecting with that portion of chamber 66 above the piston to aid in forcing piston 68 downward.

An important feature of this invention is valve 120 shown in enlarged cross-section in FIGURE 7. The valve proper is the central large diameter portion. Connected thereto are the upper and lower extensions 122 and 124. In operation, when the passageway is open, as shown in FIGURE 2, the valve is in its lowermost position. In this position there is a pressure drop across the valve body, due to constricted passage of fluid therethrough. Accordingly, thevalve is held in this position by a greater pressure-area force acting on surface 123 than the pressure-area force effective on-opposite surface 125, this latter pressure occurring through pilot opening 126. The effective areas of extensions 122 and 124 are small in relation to areas 123 and 125. The pressure difference acting on surfaces 122 and 124 tending to close the valve is insignificant, when compared with the difference across surfaces 123 and 125. This downward force holds the valve open until the force is overcome by mechanical engagement with piston 88 as it reaches the end of its upward stroke. Accordingly, the passageways through the valve body are closed, as shown in FIGURE 3. A low pressure-area force exists on the surfaces 122, 123, and 125, less than the pressure-area force existing on an extension 124, to maintain the valve closed. The valve remains closed until control rod 140, acting through sleeve 146, and piston 144, mechanically overcomes the force to open the valve and begin a new cycle.

An additional feature of this invention is the control over the rate of travel of the polish rod. The upward movement of piston 88 may be controlled by regulating .the opening of valve 36 from the pressure tank 34. Preferably, the upstroke time is at a minimum in order to reduce the time in which the hydrostatic load is operating on travelling valves and seals of a bottom-hole pump. Accordingly, maximum efliciency is accomplished regardless of pumping cycle frequency. This flexibility will allow low-productivity wells to be efliciently and profitably operated. h

Although not shown, it is within the purview of this invention that a pressure relief means of any suitable type be placed in the pressure fluid system to prevent overloading of the system in the event of excessive pressures.

The invention has been described by reference to' spe cific and preferred embodiments. It will be apparent, however, that many modifications can be made without departing from the spirit of the invention. 'Forexample, it can be readily seen that the compressible. gas used in the pneumatic spring portion of this invention can be 6 derived from a near-by source such as high pressure gas well. Accordingly, this invention should be construed not to be limited to the embodiment herein described, but should be limited only by the scope of the appended claims.

I claim:

1. In pressure fluid operated pumping mechanism a power cylinder, a first head and a second head on the cylinder, a piston movably disposed in the cylinder and connected to a polish rod slidably extended through said second head, means introducing a high pressure relatively incompressible fluid from a first source of fluid under pressure into and intermittently exhaust-ing the same from said cylinder at a relatively low pressure between said piston and said first head and means connecting the interior of the cylinder between said piston and said second head incommunication with a second source of compressible fluid under pressure.

, 2(Inpressure fluid operated pumping mechanism a power cylinder whose opposite ends are closed, a piston movably disposed in the cylinder and connected to a polish rod slidably extended through one end of the cylinder, pressure fluid filling the cylinder on opposite sides of the piston, means for causing an increase in the pressure of fluid in the cylinder on one side of the piston to move the piston in one direction and to increase the pressure of fluid in the cylinder on the other side of the piston and for causing a decrease in the pressure of fluid in the cylinder on said one side of the piston to allow the pressure of the fluid in the cylinder on said other side of the piston to move the piston in the other direc tion.

h 3. In pressure fluid operated pumping mechanism a power cylinder whose opposite ends are closed, a piston movably disposed in the cylinder and connected to a polish rod slidably extended through one end of the cylinder, said cylinder having an inlet and an outlet to a fixed chamber on one side of the piston, means for circulating fluid from a source of fluid under pressure into and out of said first chamber through said inlet and outlet, means connecting a second chamber of the cylinder on the other side of the piston in communication with another source of fluid under pressure, and means in said first chamber between said inlet and said outlet for periodically interrupting the circulating of fluid to alternately increase and decrease the pressure in said first chamber to cause the piston to reciprocate.

4. A pumping mechanism according to claim 3, wherein said source of fluid under pressure in communication with said second chamber includes a pneumatic spring.

5. In pressure fluid operated pumping mechanism a power cylinder whose opposite ends are closed, a piston movably disposed in the cylinder and connected to a polish rod slidably extended through one end of the cylinder, said cylinder having an inlet and an outlet to a first chamber on one side of the piston, means for circulating fluid from a source of fluid under pressure into and out of the said first chamber through said inlet and outlet, means in said first chamber for periodically interrupting the circulation of fluid between said inlet and outlet, to alternately increase and decrease the pressure in said first chamber on said one side of the piston, a pressure fluid filling a second chamber on the other side of the piston and means for maintaining the pressure of the fluid in said second chamber at a constant value to move the piston upon decrease of pressure in said first chamber.

6. In pressure fluid operated pumping mechanism a vertically disposed power cylinder whose opposite ends are closed, a piston movably disposed in the cylinder and connected to a polish rod slidably extended through the lower end of the cylinder, said cylinder having an inlet and outlet above the piston, means for circulating a fluid under pressure through said inlet and outlet, a valve body in the cylinder above the piston and having a passageway and valve port formed in the passageway through which fluid may flow from the inlet to the outlet, a valve movably positioned in the body for movement into and out of a position to close said port, a pressure fluid filling the cylinder beneath the piston, means for applying pressure fluid in cylinder beneath the piston, means for closing the valve to cause an increase in the pressure of fluid in the cylinder above the piston to move the piston downwardly and for opening the valve to cause a decrease in the pressure of fluid in the cylinder above the piston to allow the piston to move upwardly under the influence of the pressure in the cylinder beneath the piston.

7. In pressure fluid operated pumping mechanism a vertically disposed power cylinder whose opposite ends are closed, a piston movably disposed in the cylinder and connected to a polish rod slidably extended through the lower end of the cylinder, said cylinder having an inlet and an outlet above the piston, means for circulating a fluid under pressure through said inlet and outlet, a valve body in the cylinder above the piston and having a passageway through which fluid may flow from said inlet to said outlet, a valve movably positioned in the body for movement into and out of aposition to close said passageway, pressure fluid filling the cylinder beneath the piston, means positioned for coaction with the valve and piston to close the valve when the piston reaches its uppermost position in the cylinder to cause an increase in the pressure fluid in the cylinder above the piston to move the piston downwardly and to increase the pressure of fluid in the cylinder beneath the piston and means positioned for coaction with the valve and piston to open the valve when the piston reaches its lowermost position in the cylinder to cause a decrease in the pressure of fluid in the cylinder above the piston to move the piston upwardly under the influence of the pressure of fluid in the cylinder beneath the piston.

8. In pressure fluid operated pumping mechanism a vertically disposed power cylinder whose opposite ends are closed, a piston movably disposed in the cylinder and connected to a polish rod slidably extended through the lower end of the cylinder, said cylinder having inlet and outlet port means on one side of the piston, means for circulating a fluid under pressure through said port means, a valve body in the cylinder on said one side of the piston and having a passageway through which fluid may flow from said inlet port means to said outlet port means, a valve movably positioned in the body for movement into and out of a position to close said passageway and having a first portion extending on one side of the body when the valve is closed and a second portion extending on the other side of the body when the valve is open, a control rod on the piston and slidably extended through the body, pressure fluid filling the cylinder on the other side of the piston, said piston being engageable with said first portion of the valve to close the valve upon movement of the piston in an upward direction in the cylinder to cause an increase in the pressure of fluid on said one side of the piston to move the piston in a downward direction to increase the pressure of fluid in the cylinder on the other side of the piston and means positioned for coaction with said control rod and said second portion of the valve upon movement of the piston in said downward direction to open the valve to cause a decrease in the pressure of fluid on said one side of the piston to allow the piston to move in said upward direction under the pressure of fluid in the cylinder on said other side of the piston.

9. In pressure fluid operated pumping mechanism a vertically disposed power cylinder whose opposite ends are closed, a piston movably disposed in the cylinder and connected to a polish rod slidably extended through the lower end of the cylinder, said cylinder having an inlet and an outlet above the piston, means for circulating a fluid under pressure through said inlet and outlet, a valve body in the cylinder above the piston and having a passageway and a valve seat formed in the passageway through which fluid may flow from the inlet to the outlet, a valve movably positioned in the body for movement to one position to close said passageway and to another position to open the passageway, pressure fluid filling the cylinder beneath the piston, means for moving the valve to closed position to cause an increase in the pressure of fluid in the cylinder above the piston to move the piston downwardly therebyincreasing the pressure of fluid in the cylinder beneath the piston and to open position to cause a decrease in the pressure of fluid in the cylinder above the piston to allow the pressure in the cylinder beneath the piston to move the piston upwardly, said valve having a first cross-sectional area which is positioned to be exposed to the pressure of fluid in the cylinder above the piston and operable when the valve is closed to hold the valve in the closed position by the pressure of fluid in the cylinder above the piston during downward movement of the piston, said valve having a second cross-sectional area exposed to the pressure of fluid in the cylinder above the piston and operable when the valve is open to hold the valve in the open position by the pressure of fluid in the cylinder above the piston during upward movement of the piston.

10. A pumping mechanism according to claim 9, wherein said first and second cross-sectional areas are oppositely facing.

11. In pressure fluid operated pumping mechanism a vertically disposed power cylinder whose opposite ends are closed, a piston movably disposed in the cylinder and connected to a polish rod slidably extended through the lower end of the cylinder, said cylinder having an inlet and an outlet above the piston, means for circulating a fluid under pressure through said inlet and outlet, a valve body in the cylinder above the piston having a passageway and a valve seat formed in the passageway through which fluid may flow from the inlet to the outlet, a valve movably positioned in the body for movement to one position to close said passageway and to another position to open the passageway, pressure fluid filling the cylinder beneath the piston, means for moving the valve to closed position to cause an increase in the pressure of fluid in the cylinder above the piston to move the piston downwardly thereby increasing the pressure of fluid in the cylinder beneath the piston and to open position to cause a decrease in the pressure of fluid in the cylinder above the piston to allow the pressure in the cylinder beneath the piston to move the piston upwardly, said valve having a first cross-sectional area which is positioned to be exposed to the pressure of fluid in the cylinder above the piston and operable when the valve is closed to hold the valve in the closed position by the pressure of fluid in the cylinder above the piston during downward movement of the piston, said valve having a second cross-sectional area exposed to the pressure of fluid in the cylinder above the piston and operable when the valve is open to hold the valve in the open position by the pressure of fluid in the cylinder above the piston during upward movement of the piston, and means coacting with said piston to throttle the flow of pressure fluid to said outlet when said piston is near the beginning and near the end of its upward movement.

12. In pressure fluid operated pumping mechanism, a vertically disposed power cylinder having upper and lower heads closing the opposite ends of the cylinder, a piston reciprocable in the cylinder connected to a pump rod s1idably extended through the lower head, means for circulating fluid from a source of fluid under pressure into and rrom the portion of the cylinder above the piston to urge the piston downwardly in the cylinder, and pneumatic spring means operably connected to the piston to alternately store energy resulting from downward movement of said piston and to re-exert the stored energy to elevate the piston.

13 A pumping mechanism according to claim 12, wherein said pneumatic spring means comprises a chamher, a passageway providing communication between the chamber and the portion of the cylinder below the piston, a body of hydraulic fluid filling the said latter portion of the cylinder, said passageway and a portion of said chamher, and a body of pneumatic fluid confined under a predetermined pressure in the remaining portion of the chamber.

14. A pumping mechanism according to claim 13, wherein said pneumatic spring means includes means for maintaining a constant predetermined pressure of the pneumatic fluid in the chamber.

15. In pressure fluid operated pumping mechanism, a vertically disposed power cylinder having upper and lower heads closing the opposite ends of the cylinder, a piston reciprocable in the cylinder connected to a pump rod slidably extended through the lower head, said cylinder having an inlet and an outlet above the piston, means for circulating fluid from a source of fluid under pressure into and out of said cylinder through said inlet and outlet, means in the cylinder between the inlet and outlet for periodically interrupting the circulation of fluid out of said cylinder to alternately increase and decrease the pressure in the cylinder above the piston to permit the piston to reciprocate, and pneumatic spring means operably connected to the piston to alternately store energy resulting from downward movement of said piston and to re-exert the stored energy to elevate the piston.

16. A pumping mechanism according to claim 15, wherein said pneumatic spring means comprises a chamber, a passageway providing communication between the chamber and the portion of the cylinder below the piston, a body of hydraulic fluid filling the said latter portion of the cylinder, said passageway and a portion of said chamber, and a body of a pneumatic fluid confined under a predetermined pressure in the remaining portion of the chamber.

17. A pumping mechanism according to claim 16, wherein said pneumatic spring means includes means for maintaining a constant predetermined pressure of the pneumatic fluid in the chamber.

18. In pressure fluid operated mechanism a power cylinder whose opposite ends are closed, a piston movably disposed in the cylinder, said cylinder having an inlet and an outlet on a first side of the piston, means for circulating fluid from a source of fluid under pressure into and out of said cylinder through said inlet and outlet, means connecting the interior of the cylinder on a second side of the piston in communication with another source of fluid under pressure, means for applying a load to the piston to urge the piston in a direction to increase the pressure in the cylinder on said second side of said piston and means in the cylinder between said inlet and said outlet for periodically interrupting the circulation of fluid out of the cylinder to alternately increase and decrease the pressure in the cylinder on said first side of the piston to alternately move the piston in one direction under the influence of said load and the pressure in the cylinder on said first side and in the other direction under the influence of the pressure in the cylinder on said second side of said piston.

19. In pressure fluid operated mechanism a power cylinder whose opposite ends are closed, a piston movably disposed in the cylinder, said cylinder having an inlet and an outlet on one side of the piston, means for circulating fluid from a source of fluid under pressure into and out of said cylinder through said inlet and outlet, valve means in the cylinder located in the path of flow between said inlet and said outlet and including a valve movable to one position to interrupt the flow of fluid from said inlet toward said outlet and to another position to permit such flow, means for closing said valve in response to a predetermined movement of said piston in one direction and for opening the valve in response to a predetermined movement of the piston in the other direction and means for yieldingly urging the piston in said one direction.

20. A hydraulic engine comprising a power cylinder, a power piston in said cylinder, a cylinder head in one end of said cylinder, said head and said piston forming a variable volume chamber for power fluid in said cylinder, means separated from said power fluid for urging said piston toward said cylinder head, means for introducing said power fluid into said chamber to force said piston away from said cylinder head and means for exhausting said power fluid from between said piston and said cylinder head to cause said piston to move toward said cylinder head.

21. A hydraulic engine comprising a power cylinder, a power piston in said cylinder, a cylinder head in one end of said cylinder, said head and said power piston forming a variable volume chamber for power fluid in said cylinder, means separated from said power fluid for urging said power piston toward said head, means for attaching a load to said power piston, a power fluid inlet to said cylinder through said cylinder head, a power fluid outlet through said cylinder head in fluid communication with said inlet, means for closing off said outlet from said inlet to cause said power piston to move away from said cylinder head and means for opening said inlet to cause said piston to move toward said cylinder head.

22. A fluid powered engine comprising a power cylinder, a power piston in said cylinder, a cylinder head in one end of said cylinder, said piston being free to be moved longitudinally in said cylinder, means for urging said power piston toward said cylinder, a power fluid inlet to said power cylinder through said cylinder head, a power fluid outlet from said power chamber through said cylinder head in fluid communication with said inlet, a valve between said inlet and said outlet, means for closing said valve to cause power fluid to move said power piston away from said cylinder head and means for opening said valve to exhaust power fluid from between said power piston and said cylinder head to allow the power piston to move toward said cylinder head under the action of said urging means.

23. A hydraulic engine comprising a power cylinder, a cylinder head on each end of the cylinder, a stationary head in the cylinder intermediate said cylinder heads and having a passageway therethrough, from one side to the other side of said stationary head, a piston movably disposed in the cylinder between said stationary head and one of said cylinder heads, said cylinder having a power fluid inlet in said stationary head in communication with said passageway and a power fluid outlet in communication with said inlet through said passageway, a valve movably disposed in said passageway for movement to one position to shut off the flow of power fluid from said inlet to said outlet through the passageway and to another position to permit such flow, means for moving the valve from said one to said other of said positions to admit power fluid to said cylinder between said stationary head and said piston to cause the piston to move away from said stationary head said movement of said piston to energize force means separated from said power fluid and means for moving said valve to said other position to permit the outflow of power fluid from between the stationary head and said piston to allow the piston to move toward said stationary head by said force means.

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